1. Field of the Invention
This invention relates to a releasable balloon catheter, and more specifically, to a releasable balloon catheter for use in occluding or embolizing a vascular lesion.
2. Description of the Prior Art
Catheters have been used as essential medical instruments for diagnosis and treatment. In recent years, it has been made possible to insert a so-called balloon catheter having at its tip an inflatable and shrinkable balloon into the inside of a minute vessel along a blood stream, which cannot be reached by means of conventional catheters not provided with a balloon. This has further increased the range of application of catheters.
If an inflated balloon can be released from the tip of a catheter at the desired site, the treatment of various vascular lesions, which has been impossible by conventional techniques, will be able to be achieved. An example is the application of balloon catheters to the treatment of aneurysm, arteriovenous malformation and arteriovenous fistula which are typical vascular disorders. For example, by keeping an inflated balloon within an aneurysm, a serious sequela in the event of rupture of the aneurysm can be prevented. Or by occluding a vessel leading to a malformed arteriovein with a released ballon, a sequela of arteriovenous malformation incident to bleeding can be prevented. Furthermore, if an arteriovenous fistula can be occluded, the blood flow in an artery can be restored to one close to a normal condition.
As is clear from a few examples given herein, if a catheter having a releasable balloon is developed, it will be a great boon to patients suffering from cerebrovascular disorders and cardiovascular disorders which occupy the first and third places, respectively, of mortality in Japan. The great significance of the development of such a catheter is clear in view of the fact that this new method of treatment does not require any surgical operation, but can be achieved simply by injection.
The site at which the balloon is desired to be released is mainly a vascular lesion which is located deep inside the body. Accordingly, it is required that the balloon should not be released from the main portion of the catheter until it reaches this site, and that the balloon should be released even at such a site which is deep inside the body.
Prior to the present invention, two types of catheter with a releasable balloon have been devised for vascular occlusion. In one type, first reported by Debrun (Neuroradiology 1975, 9:267.about.271 and J. Neurosurgery 1978, 49:635.about.649), the balloon is firmly tied to a Teflon catheter with elastic threads and is released with the help of a second coaxial polyethylene catheter. The disadvantage of this type is that the catheter is difficult to introduce beyond many arterial curves such as the carotid siphon, because of its lack of flexibility. Its use also requires a relatively large coaxial catheter. The other has been reported by Serbinenko (U. Neurosurgery 1974, 41:125.about.145), who attaches a balloon to a polyethylene catheter which grips the catheter due to its elasticity. The balloon is released simply by pulling on the catheter. This type of catheter can be used with lesions on many branches of the arterial tree. It has the danger that it can be released accidentally. It can also damage the vascular lesion if it is pulled on.
An attempt was made to remedy these defects. Japanese Laid-Open Patent Publication No. 132580/1977 discloses a balloon catheter in which the balloon is fixed to the main portion of the catheter by securing a C-type spring to a joint part between them. In such a balloon catheter, the C-type spring is released when the pressure in the balloon exceeds a specified limit by the pressure of a fluid introduced into the balloon. Thus, the balloon is released from the catheter. However, the balloon catheter of this type has the disadvantage that there are some cases where the balloon is released in a place other than the desired site and cannot be released when desired, because it is difficult to adjust the pressure applied by the C-type spring.